Effect of electrically aligned polycrystalline diamond flakes on the through-plane thermal conductivity of heat conduction sheets

Heat conduction sheets, which are composed of a thermally conductive filler and a base elastomer matrix, are important for dissipating heat from devices to a heat sink. Alignment of the heat-conducting two-dimensional filler particles enhances the thermal conductivity of the heat conduction sheet. In this study, we prepared polycrystalline diamond (PCD) flakes and then electrically aligned the PCD flakes in the through-plane direction of heat conduction sheet samples. The PCD flakes were fabricated by pulverizing a synthesized PCD thin layer. The typical size of the PCD flakes was ∼1 μm in thickness and ∼35 μm in diameter. The PCD flakes were electrically aligned in a polydimethylsiloxane (PDMS) matrix by applying alternating high voltage with parallel-plate electrodes. The heat conduction sheet containing 20 wt% aligned PCD flakes in the matrix exhibited high through-plane thermal conductivity of 0.47 W m⁻¹ K⁻¹, while that of the heat conduction sheet with aligned granular diamond filler particles was 0.37 W m⁻¹ K⁻¹. The high thermal conductivity comes from the formation of a large contact area between the filler particles and flake network by electrical alignment in the heat conduction sheet.